Scale-Up of Laminar Coflow Method for Selective Precipitation from Micro- to Millifluidics

Abstract The laminar coflow method (LCM) is a promising separation approach that allows selective precipitation of minerals from complex feedstocks. LCM offers unique process control, leading to high product purity and selectivity, but the method is in early stages of research with reported studies currently limited to experiments in microfluidic devices at low flow rates. Commercial implementation of LCM for critical mineral separation will require the scale-up of coflow reactors through a combination of numbering-up and scaling-up to meet the flow rates required for industrial-scale processing. In this study, we experimentally evaluated LCM scale-up using the selective precipitation of Mg(OH)2 from seawater as a representative chemistry. We successfully demonstrated the feasibility of scaling-up LCM from microfluidic devices to the millifluidic scale without performance loss and provided the first demonstration of continuous solid collection using LCM. We used computational fluid dynamics (CFD) modeling to identify the critical scalability parameters. Our CFD model outputs showed alignment with experimental observations and that the steep concentration gradients characteristic of LCM can be achieved in reactors up to 1 m in diameter. The model also identified a <5% difference in fluid densities as a design limitation for maintaining a well-defined reactive interface for LCM. To be industrially relevant, LCM will need further scale-up from millifluidics, and this is the first step toward designing larger LCM reactors.